Due to the great importance for many industrial applications it is crucial from the point of view of theoretical description to reproduce thermal properties of thermoplastic polyimides as accurate as possible in order to establish "chemical structure-physical properties" relationships of new materials. In this paper we employ differential scanning calorimetry, dilatometry, and atomistic molecular dynamics (MD) simulations to explore whether the state-of-the-art computer modeling can serve as a precise tool for probing thermal properties of polyimides with highly polar groups. For this purpose the polyimide R-BAPS based on dianhydride 1,3-bis(3',4-dicarboxyphenoxy)benzene (dianhydride R) and diamine 4,4'-bis(4''-aminophenoxy)biphenyl sulphone) (diamine BAPS) was synthesized and extensively studied. Overall, our findings show that the widely used glass-transition temperature Tg evaluated from MD simulations should be employed with great caution for verification of the polyimide computational models against experimental data: in addition to the well-known impact of the cooling rate on the glass-transition temperature, correct definition of Tg requires cooling that starts from very high temperatures (no less than 800 K for considered polyimides) and accurate evaluation of the appropriate cooling rate, otherwise the errors in the measured values of Tg become undefined. In contrast to the glass-transition temperature, the volumetric coefficient of thermal expansion (CTE) does not depend on the cooling rate in the low-temperature domain (T < Tg) so that comparison of computational and experimental values of CTE provides a much safer way for proper validation of the theoretical model when electrostatic interactions are taken into account explicitly. Remarkably, this conclusion is most likely of generic nature: we show that it also holds for the commercial polyimide EXTEM, another polyimide with a similar chemical structure.

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Experimental results have shown that graphitizated carbon nanofibers initiate crystallization in R-BAPB polyimides twice as fast as single-wall carbon nanotubes (CNT) leading to the hypothesis that nanofiller curvature influences polyimide crystallization. Therefore, atomistic molecular-dynamics simulations have been performed for R-BAPB in the presence of a flat graphene sheet and the results were compared with those obtained in the presence of a small-radius CNT. The polyimide chain segments tend to lie parallel to the nanofiller surface and this tendency is stronger and the segments are closer to the graphene surface than to the CNT one. Moreover, the density of the polyimide in the near-surface layer is higher for composites filled with graphene than with CNT. This confirms the assumption that the nanofiller surface curvature is indeed a factor influencing the polymer patterning structure, and that a smaller curvature (i.e. flat surface) provides an enhanced initiation of polymer ordering. A IntroductionOne of the most promising ways to improve the performance of polymeric materials consists of developing polymer composites.1-3 Signicant changes aer addition of a ller are inuenced by the polymer and ller properties, but also by the interface interactions between both components. The use of nanoscalereinforcing llers leading to a considerable increase in the interaction area between the composite components has driven the interest of researchers in last years.4-11 Allotropic carbon compounds (carbon black, fullerenes, single-and multiwall nanotubes, nanobers and graphene sheets) are among the popular nanollers. 4,7,9,[11][12][13][14][15][16][17] Polymers with a relatively simple or complicated molecular structure have been and are currently used as matrices in nanocomposite materials. 4,[17][18][19] By combining different types of matrices and nanollers, it is possible to obtain composites with a wide range of physical properties. In some cases, a nanoller can initiate the crystallization of the polymer matrix, 18,20-25 signicantly accelerating the formation of crystallites, or even initiating their formation in the polymer under conditions which do not normally favor the crystallization, as in the case of ODPA-P3 polyimide.26 Crystallization of a polymer matrix in a nanocomposite may signicantly impact its mechanical and thermophysical properties, which should be taken into account when developing new composite materials.18,27,28 The advantage of using nanoparticles for initiation of crystallization is that the formation of a large number of nanoscale crystallites improves the strength of the nanocomposite preventing the typical failure on the boundary area between crystalline regions, thus improving the performance of the material. Therefore, the question arises on how the physical properties of carbon nanollers affect the initiation of crystallization in semicrystalline thermoplastic matrices.Yudin et al. 17,[23][24][25]29 investigated the crystallization initiation of the semicrystalline ther...

Summary: The relatively high degree of crystallinity of a new thermoplastic polyimide (PI) makes it a favorable matrix candidate for fiber reinforced composites. This advantage is the result of the ability of the matrix to recrystallize during the composite manufacturing process. In this study we examine the potential nucleating effect of carbon nanotubes on a thermoplastic PI. In addition to their inherent mechanical contribution, the carbon nanotubes help recover a significant proportion of the original crystallinity.Scanning electron micrograph of the spherulitic structure of a recrystallized carbon nanotube/polyimide film.magnified imageScanning electron micrograph of the spherulitic structure of a recrystallized carbon nanotube/polyimide film.

Abstract:The paper describes the process to produce Chitin Nanofibril-Hyaluronan nanoparticles (CN-HA), showing their ability to easily load active ingredients, facilitate penetration through the skin layers, and increase their effectiveness and safety as an OPEN ACCESSCosmetics 2014, 1 141 anti-aging agent. Size and characterization of CN-HA nanoparticles were determined by Scanning Electron Microscopy (SEM) and Zetasizer, while encapsulation efficiency and loading capacity of the entrapped ingredients were controlled by chromatographic and spectrophotometric methods. Safeness was evidenced on fibroblasts and keratinocytes culture viability by the MTT (Methylthiazol) assay; anti-aging activity was evaluated in vitro measuring antioxidant capacity, anti-collagenase activity, and metalloproteinase and pro-inflammatory release; efficacy was shown in vivo by a double-blind vehicle-controlled study for 60 days on 60 women affected by photo-aging. In addition, the CN-HA nanoparticles have shown interesting possibility to be used as active ingredients, for designing and making advanced medication by the electrospinning technology, as well as to produce transparent films for food packaging, by the casting method, and can be used also in their dry form as tissues or films without adding preservatives. These unusual CN-HA nanoparticles obtained from the use of raw materials of waste origin may offer an unprecedented occasion for making innovative products, ameliorating the quality of life, reducing pollution and safeguarding the environment's integrity.

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New semicrystalline polyimide/oligoimide blends, designated for matrices in carbon fiber-reinforced composites, were developed. A specific advantage of the proposed polyimides is their ability to crystallize from the melt, therein retaining their crystallinity throughout the manufacturing process. The generation of crystallinity after melting, referred to as recrystallization, was investigated here as affected by blending the polyimides with oligoimides of a similar chemical structure. Based on thermal analysis and enthalpy measurements, comparative X-ray diffraction analyses, and polarized light microscopy of hot-stage-controlled crystallization, the recrystallization ability was determined for five different oligoimides. In some cases, the addition of oligoimides, both amorphous and crystalline, resulted in complete recrystallization. The main contribution of the oligoimides is suggested to be through plasticization, allowing segmental chain mobility during crystallization, and not via nucleation. A similar effect was obtained by lowering the molecular weight of the polyimide; this, however, generates mechanical property reduction, rendering the polyimide irrelevant to composite materials. Finally, it was shown that crystallization was also enhanced by carbon fibers, serving as a nucleating agent and generating transcrystallization.

The surgical face mask (SFM) is a sheet medical device covering the mouth, nose and chin to protect the medical staff from the spread of respiratory droplets produced by the infective coughing or sneezing of hospitalized patients. On the other hand the beauty face mask (BFM) has been made by the same sheet but with a different aim—to protect the skin from pollution, acting as a hydrating and rejuvenation agent. Currently, both masks are made principally by non-biodegradable tissues, utilized to avoid the increasing great pollution invading our planet. Due to the diffusion of the current COVID-19 infection rate and the increasing consumption of skin care and beauty products, the waste of these masks, made principally by petrol-derived polymers, is creating further intolerable waste-invaded land and oceans. After an introduction to the aims, differences and market of the various masks, their productive means and ingredients are reported. These news are believed necessary to give the reader the working knowledge of these products, in the context of the bioeconomy, to better understand the innovative tissues proposed and realized by the biobased and biodegradable polymers. Thus, the possibility of producing biodegradable SFMs and BFMs, characterized for their effective antimicrobial and skin repairing activities or hydrating and antiaging activity, respectively. These innovative smart and biodegradable masks are requested from the majority of consumers oriented towards a future green environment. Giving this new sense of direction to their production and consumption, it will be possible to reduce the current waste, ranging worldwide at about 2 billion tons per year.